1. Field of the Invention
The present invention relates to a novel steam turbine of high efficiency and high temperature, and more particularly to a steam turbine in which a main steam temperature and/or a reheat steam temperature are/is 620 (.degree. C.) or above. It also relates to a steam-turbine power plant which employs such steam turbines.
2. Description of the Related Art
Conventional steam turbines have had a steam temperature of 566 (.degree. C.) at maximum and a steam pressure of 246 (atg).
It is desired, however, to heighten the efficiencies of thermal power plants from the viewpoints of the exhaustion of fossil fuel such as petroleum and coal, the saving of energy, and the prevention of environmental pollution. For enhancing the power generation efficiencies, it is the most effective expedient to raise the steam temperatures of the steam turbines. Regarding materials for such high-efficiency turbines, 1Cr--1Mo--1/4V ferritic low-alloy forged steel and 11Cr--1Mo--V--Nb--N forged steel are known as rotor materials, while 1Cr--1Mo--1/4V ferritic low-alloy cast steel and 11Cr--1Mo--V--Nb--N cast steel are known as casing materials. Among these materials, austenitic alloys disclosed in the official gazette of Japanese Patent Applications Laid-open No. 180044/1987 and No. 23749/1986, and martensitic steel disclosed in the official gazette of Japanese Patent Applications, Laid-open No. 147948/1992, No. 290950/1990 and No. 371551/1992 are especially known as materials whose high-temperature strengths are superior.
Although, in the laid-open applications mentioned above, the rotor materials, the casing materials, etc. are disclosed, almost no consideration is given to the steam turbines and the thermal power plants which are accompanied by the higher steam temperatures as stated above.
Further, a supercritical steam turbine is known from the official gazette of Japanese Patent Applications, Laid-open No. 248806/1987, but a plant system as a whole is not considered at all.